The invention relates to an apparatus for optimizing the running or operating characteristics of tires or wheels comprising rims with tires secured thereto.
Such machines are well known in the art as so-called force measuring balancing machines. In such machines the output signals of vibration sensors and the output signals of angular position pick-ups are multiplied, for example, in a known manner by means of a watt meter or the like. However, it is also possible to perform the multiplication by means of an electronic multiplier. Force measuring balancing machines determine the unbalance or imbalance of a tire at a given mean speed in the order of about 50 kilometers per hour. By multiplying the output signals of the vibration sensors and of the angular position pick-up, it is possible to eliminate disturbances, that is, forces which do not have the frequency corresponding to the r.p.m. or rotational frequency.
U.S. Pat. No. 3,527,103 discloses a machine for measuring the tire uniformity. In this apparatus force vibrations are measured at a constant r.p.m. or speed and the respective Fourier coefficients are determined for the desired harmonic, whereby it is possible to determine the size and phase position of any deviation. Based on these results the tire may be corrected by applying or removing rubber to or from the tire. The structure of the apparatus according to U.S. Pat. No. 3,527,103 requires operation at a constant measuring speed. Such measuring speed must be relatively low in order to provide an indication, especially of the phase angle which is at least somewhat accurate.
An article entitled "Uniformity Testing of Tires" which appeared in "Automobiltechnische Zeitschrift 77" (1975) Number 2, pages 46 to 49 describes an apparatus for determining the tire uniformity in which the force variations related to selectable rotational angles of the tire are measured or determined and stored in a computer. The stored values are then digitized and used for calculating the Fourier coefficients of the first or higher harmonic of the force variations. This machine for the uniformity control of a tire production is highly precise. However, this known apparatus can be manufactured in a economic way only if again relatively low measuring speeds are satisfactory.
It has been found that low measuring speeds or rather low circumferential speeds necessary for such low measuring speeds are disadvantageous because the tire non-uniformity and unbalance may change at higher tire rotational speeds due to inhomogenities of the tire rubber. Thus, it is desirable to perform the testing at speeds which simulate the actual rotational speeds when a tire is used on a vehicle travelling on a road.